Biology of Autogenous Horse Flies Native to Coastal California: Apatolestes actites (Diptera: Tabanidae)

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Abstract
At a sandy ocean beach in Marin County, Calif., immatures of the pangoniine horse fly, Apatolestes actites Philip and Steffan, inhabited the supralittoral zone to depths of 8 to 36 cm in relatively saline soil that is aridic for at least 6 months yearly. Adults flew from early June to mid-July. Flies emerged between 0751 and 1258 h (PST); they dispersed to the littoral/lower supralittoral zones, where they basked up to 3 h and then disappeared. Only gravid females returned to the beach area, where parous flies apparently remained after ovipositing. Longevity of confined, newly emerged males and females averaged 5.0 (2–11) and 9.3 (4–17) days, respectively. Females developed their first batch of eggs autogenously in 6 days at 25°C and 67% relative humidity (RH); four wild-caught flies had also produced, or were in the process of developing, a second batch of eggs autogenously. Fecundity averaged 322 (218–415, n = 8) eggs in the first gonotrophic cycle, and 43 (32–54, n = 2) in the second. Eggs hatched in 6 to 8 days, and the mean fertility of three masses was 69%. Females laid their eggs in amphipod or isopod burrows, and rarely in driftwood. This is the first tabanid species known to oviposit subterraneously. The mandibular and maxillary stylets of female A. actites are much reduced and, presumably, unable to pierce the skin of vertebrates. The barn swallow, Hirundo rustica L., the most important predator of A. actites adults, captured newly emerged flies resting on the sand or those they had flushed off the beach by swooping down on them. The song sparrow, Melospiza melodia (Wilson), picked teneral adults off the sand near emergence sites in the upper supralittoral.